1. Field
Example embodiments relate to substrate structures and methods of manufacturing the same.
2. Description of the Related Art
Nitride-based semiconductors such as GaN are applied to light emitting devices such as blue purple light emitting diodes or laser diodes, and high-speed and high-output electronic devices. Also, white LEDs based on GaN semiconductors and fluorescent materials are widely used. GaN-based LEDs are manufactured mainly on a 2-inch sapphire substrate. However, development of GaN-based LEDS manufactured on a 4-inch sapphire substrate has started and is currently in initial stages.
In order to increase production of LEDs and reduce the unit cost of production, a large-sized substrate is needed. Sapphire substrates are expensive and have low thermal conductivities. For example, when at a high temperature, such as when growing a semiconductor layer over a wide area, the substrate may be bent. Accordingly, it is difficult to maintain uniformity.
Recently, there has been interest in use of silicon substrates in GaN-based light emitting devices. Silicon substrates are cheaper than sapphire substrates and silicon carbide (SiC) substrates and a 12″ large-caliber wafer may be used. Also, the cost price may be reduced and production of GaN-based light emitting devices may be increased by using silicon substrates. In addition, as silicon substrates have conductivity, electrodes may be formed on a lower surface of a silicon substrate and thus a manufacturing process thereof may be relatively simple. Moreover, silicon substrates have higher thermal conductivity than sapphire substrates and thus may be bent less at a high temperature for growing a GaN thin film, and thus uniform thin film characteristics may be obtained in a 8-inch substrate.
However, problems regarding high dislocation density, cracks, and optical adsorption occur with the silicon substrate due to great differences in lattice constants and coefficients of thermal expansion between the silicon substrate and a GaN thin film layer. Accordingly, various methods of reducing stress between the silicon substrate and the GaN thin film layer so as to reduce cracks and dislocation density have been suggested.